An Iranian opposition website said eight opposition supporters were killed on Sunday during clashes with police in Tehran and other cities such as Tabriz and Qom. Police shot dead three protesters in central Tehran and a fourth demonstrator was killed later in the capital, reformist websites said.

Earlier, the Iranian authorities warned of a harsh crackdown should opposition supporters hold rallies coinciding with Sunday's religious ritual observing the 7th Century death of one of Shiite's most important saints. Opposition leader Mirhossein Mousavi's nephew was among the victims, an adviser to Mousavi said. "I express my regrets and deep condolences over the martyrdom of your nephew Ali Habibi Mousevi on Sunday," Kaleme website quoted Alireza Beheshti as saying.

According to Reuters, in the morning helicopters circled overhead and black clouds of smoke billowed into the sky over central Tehran. The pro-reform Web site Rah-e-Sabz said security forces beat protesters as they chanted anti-government slogans.Police had blocked streets leading to the center of the capital but many opposition supporters managed to break the security wall.

Another opposition web site Jaras reported protesters set one police motorbike on fire in downtown Tehran. "There are sporadic clashes in different parts of downtown Tehran, including the Khark street ... There is a mass presence of protesters. Their number is increasing," Jaras said.